What was found
LEFT HYD SYS OIL LEAKAGE WAS DETECTED ON THE SYNOPTIC DISPLAY. AT FL410 AND 1.5 HOURS OUT THE PIC ELECTED TO TURN BACK TO DEPARTURE. WITH 0.5 GALLONS OF HYD FLUID REMAINING, THE ACFT LANDED WITHOUT INCIDENT. MX DETECTED FLUID LEAKAGE FROM THE LT PYLON. UPON EXPOSURE THE LT ENGINE DRIVEN PUMP CASE DRAIN FLEXIBLE HOSE WAS FOUND TO BE LEAKING AT THE FLEX HOSE SECTION. THE LEAKAGE WAS CAUSED BY CHAFING ACTION BETWEEN THE HOSE AND PYLON BULKHEAD FS767 PORTHOLE. EVIDENCE OF ADDITIONAL CHAFING WAS FOUND AT BULKHEAD FS782 BUT NOT SUFFICIENT TO CAUSE LEAKAGE. THE PRIMARY FAILURE MODE WAS LOOSE HOSE STAND OFF CLAMPS THAT CAUSED THE HOSE TO SWING INTO CONTACT WITH THE BULKHEADS. PLEASE REF MFG IPC 29-00-02, FIG 5 PAGE 0. FLEX HOSE IS ITEM 85. CLAMP IS ITEM 95.